The work machines such as the hydraulic excavators are embedded with a hydraulic circuit that a hydraulic pump is used in common for driving a plurality of actuators. In such work machines, a large amount of the hydraulic fluid flows towards a less loaded actuator in executing a combined operation of simultaneously driving a plurality of actuators. In this case, shortage of the flow rate of the hydraulic fluid is problematic in a more loaded actuator.
To solve the problem, the well-known work machines have been configured to execute a control of reducing the opening size of the control valve for one actuator (hereinafter referred to as “a non-prioritized actuator”) in executing the combined operation than that in executing a single operation (see, Japan Laid-open Patent Application Publication No. JP-A-2006-97854). With the control, a sufficient amount of the hydraulic fluid can be supplied to the other actuator (hereinafter referred to as “a prioritized actuator”).